Dextral Spiral

Pondered a few of my shells today (I have a large collection). When discussing the way shells coil, the concept of chirality or 'handedness' arises. Most gastropod molluscs (over 90%) coil dextrally, that is clockwise if you look down on the spire from above. This also means that if you face the aperture, or open end of the shell towards you, the aperture is on the right side of the shell ('right-handed'). Some families of gastropods always coil their shells sinistrally (as usual the lefties historically get the name associated with evil!), that is anticlockwise, and the aperture is on the left ('left-handed'). Sinistrality can also occur as a genetic mutation in individuals of species from families which normally coil dextrally. The family that I study most, is renowned for producing occasional sinistral specimens, and when one is accustomed to looking at dextrally coiled shells, these sinistrally coiled shells look decidedly odd.
I will blip a few of these the next time we have a rainy day, but in the meantime here is the dextrally coiled spire of a tun shell with an artistic rendering.